Exposure apparatus and method for producing device

ABSTRACT

An exposure apparatus, wherein exposure is carried out while filling a space between a projection optical system and a substrate with a liquid, enables to suppress deterioration of a pattern image caused by any bubble in the liquid. The exposure apparatus includes a liquid supply unit  1  which fills at least a part of the space between the projection optical system and the substrate with a liquid  50 , and exposes the substrate by projecting an image of a pattern onto the substrate via the projection optical system. The liquid supply unit  1  includes a degassing unit  21  which suppresses the generation of the bubble in the liquid  50.

CROSS-REFERENCE

This application is a Continuation Application of application Ser. No.11/144,827 filed Jun. 6, 2005, which in turn is a ContinuationApplication of International Application No. PCT/JP03/015407 which wasfiled on Dec. 2, 2003 claiming the conventional priority of Japanesepatent Application No. 2002-357961 filed on Dec. 10, 2002, No.2003-002820 filed on Jan. 9, 2003, and No. 2003-049367 filed on Feb. 26,2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an exposure apparatus for exposing asubstrate with a pattern image projected by a projection optical systemin a state in which at least a part of a space between the projectionoptical system and the substrate is filled with a liquid. The presentinvention also relates to a method for producing a device based on theuse of the exposure apparatus.

2. Description of the Related Art

Semiconductor devices and liquid crystal display devices are produced bythe so-called photolithography technique in which a pattern formed on amask is transferred onto a photosensitive substrate. The exposureapparatus, which is used in the photolithography step, includes a maskstage for supporting the mask and a substrate stage for supporting thesubstrate. The pattern on the mask is transferred onto the substrate viaa projection optical system while successively moving the mask stage andthe substrate stage. In recent years, it is demanded to realize thehigher resolution of the projection optical system in order to respondto the further advance of the higher integration of the device pattern.As the exposure wavelength to be used is shorter, the resolution of theprojection optical system becomes higher. As the numerical aperture ofthe projection optical system is larger, the resolution of theprojection optical system becomes higher. Therefore, the exposurewavelength, which is used for the exposure apparatus, is shortened yearby year, and the numerical aperture of the projection optical system isincreased as well. The exposure wavelength, which is dominantly used atpresent, is 248 nm of the KrF excimer laser. However, the exposurewavelength of 193 nm of the ArF excimer laser, which is shorter than theabove, is also practically used in some situations. When the exposure isperformed, the depth of focus (DOF) is also important in the same manneras the resolution. The resolution R and the depth of focus δ arerepresented by the following expressions respectively.R=k1·λ/NA  (1)δ=±k2·λ/NA ²  (2)

In the expressions, λ represents the exposure wavelength, NA representsthe numerical aperture of the projection optical system, and k1 and k2represent the process coefficients. According to the expressions (1) and(2), the following fact is appreciated. That is, when the exposurewavelength λ is shortened and the numerical aperture NA is increased inorder to enhance the resolution R, then the depth of focus δ isnarrowed.

If the depth of focus δ is too narrowed, it is difficult to match thesubstrate surface with respect to the image plane of the projectionoptical system. It is feared that the margin is insufficient during theexposure operation. Accordingly, the liquid immersion method has beensuggested, which is disclosed, for example, in International PublicationNo. 99/49504 as a method for substantially shortening the exposurewavelength and widening the depth of focus. In this liquid immersionmethod, the space between the lower surface of the projection opticalsystem and the substrate surface is filled with a liquid such as wateror any organic solvent to utilize the fact that the wavelength of theexposure light beam in the liquid is 1/n as compared with that in theair (n represents the refractive index of the liquid, which is about 1.2to 1.6 in ordinary cases) so that the resolution is improved and thedepth of focus is magnified about n times.

Any bubble sometimes adheres to the lower surface of the projectionoptical system and/or the substrate surface in the state in which thespace between the lower surface of the projection optical system and thesubstrate surface is filled with the liquid. In this way, for example,if the bubble exists in the liquid disposed between the projectionoptical system and the substrate during the exposure, the followingphenomenon arises. That is, for example, the light beam, which isradiated to form the image on the substrate, does not arrive at thesubstrate surface, and/or the light beam, which is radiated to form theimage on the substrate, does not arrive at a desired position on thesubstrate. As a result, the pattern image, which is to be formed on thesubstrate, is deteriorated.

SUMMARY OF THE INVENTION

The present invention has been made taking the foregoing circumstancesinto consideration, an object of which is to provide an exposureapparatus which makes it possible to suppress the deterioration of apattern image which would be otherwise caused by any bubble in a liquidwhen the exposure process is performed while filling a space between aprojection optical system and a substrate with the liquid, and a methodfor producing a device based on the use of the exposure apparatus.

In order to achieve the object as described above, the present inventionadopts the following constructions corresponding to FIGS. 1 to 7 asillustrated in embodiments.

According to a first aspect of the present invention, there is providedan exposure apparatus which exposes a substrate with an image of apredetermined pattern, the exposure apparatus comprising:

a projection optical system (PL) which projects the image of thepredetermined pattern onto the substrate;

a liquid supply unit (1) which supplies a liquid to a space between theprojection optical system and the substrate; and

a gas-removing unit (21) which removes a gas component contained in theliquid which is to be supplied to the space between the projectionoptical system and the substrate.

In the exposure apparatus of the present invention, the liquid, fromwhich the gas component has been sufficiently removed, can be suppliedto the space between the projection optical system and the substrate,because the exposure apparatus of the present invention is provided withthe gas-removing unit which removes the gas component from the liquid.Further, the generation of the bubble is suppressed not only in theliquid existing between the projection optical system and the substrate(in the optical path for the exposure light beam) but also in the liquidexisting in the liquid flow passage running from the gas-removing unitto the space between the projection optical system and the substrate.The gas-removing unit removes the gas component from the liquid so thatan air concentration in the liquid is desirably not more than 0.016cm³/cm³. Those usable as the gas-removing unit include a heating unit, apressure-reducing unit, a degassing membrane, and a combination thereof.The gas-removing unit may be arranged in the liquid supply unit oroutside the liquid supply unit. Alternatively, the gas-removing unit maybe arranged outside a chamber of the exposure apparatus.

The liquid supply unit may include a plurality of supply nozzles whichsupply the liquid to the space between the projection optical system andthe substrate, and a plurality of recovery nozzles which recover theliquid supplied to the space between the projection optical system andthe substrate. When the plurality of nozzles are used, it is possible touniformly supply the liquid to the projection area. The exposureapparatus may further comprise a stage which is movable while placingthe substrate thereon. The exposure may be performed during a period inwhich the stage moves the substrate with respect to the image projectedfrom the projection optical system (scanning exposure). In thisprocedure, it is preferable that the supply nozzles jet the liquid in adirection of movement of the substrate, in view of the fact that theinflow resistance of the supply liquid is lowered to exert no influenceon the movement of the stage.

The exposure apparatus of the present invention may further comprise atemperature-adjusting unit which adjusts a temperature of the liquidsupplied from the liquid supply unit. It is desirable that thetemperature-adjusting unit adjusts the temperature of the liquid so thatthe temperature of the liquid is a temperature in the exposureapparatus, for example, an atmospheric temperature in a chamber foraccommodating the exposure apparatus. Accordingly, a temperature of thesubstrate may be controlled by supplying the temperature-adjusted liquidto the space between the projection optical system and the substrate.

According to a second aspect of the present invention, there is providedan exposure apparatus (EX) which exposes a substrate (P) by projectingan image of a pattern onto the substrate with a projection opticalsystem (PL), the exposure apparatus (EX) comprising:

a liquid supply unit (1) which fills, with a liquid (50), at least apart of a space between the projection optical system (PL) and thesubstrate (P); and

a bubble-suppressing unit (21) which suppresses generation of any bubblein the liquid.

According to the present invention, the bubble-suppressing unit isprovided, which suppresses the generation of the bubbles in the liquidbetween the projection optical system and the substrate. Therefore, theexposure process can be performed in a state in which no bubble existsin the liquid on the optical path for the exposure light beam.Accordingly, it is possible to avoid the deterioration of the patternimage which would be otherwise caused by the bubble. It is possible toproduce a device having a high pattern accuracy. For example, when thebubble-suppressing unit, which suppresses the generation of the bubblein the liquid, is provided for the liquid supply unit which supplies theliquid to the space between the projection optical system and thesubstrate, the liquid can be supplied to the space between theprojection optical system and the substrate after sufficientlysuppressing the generation of the bubble in the liquid. Therefore, nobubble is generated from the liquid which fills the space between theprojection optical system and the substrate. Even if any bubble isgenerated in the flow passage through which the liquid flows, including,for example, the lower surface of the projection optical system and thesurface of the substrate, then the liquid, in which the generation ofthe bubble is sufficiently suppressed, flows through the flow passage,and thus the liquid can absorb and remove the bubble generated in theflow passage. As described above, the exposure process can be performedin the state in which no bubble exists in the liquid on the optical pathfor the exposure light beam. Therefore, it is possible to avoid thedeterioration of the pattern image which would be otherwise caused bythe bubble. It is possible to produce a device having a high patternaccuracy.

In the exposure apparatus of the present invention, it is preferablethat the bubble-suppressing unit includes a degassing unit which removesany gas from the liquid. It is preferable that the degassing unitincludes a heating unit which heats the liquid. The heating unit may seta temperature T of the liquid to be 30° C.<T≦100° C. Further, thedegassing unit may include a pressure-reducing unit which reduces apressure in a unit in which the liquid is retained. Thepressure-reducing unit may set the pressure depending on a temperatureof the liquid. Further, it is preferable that the degassing unitdetermines a degassing level so that the bubble is not generated by anychange in temperature of at least a part of the liquid disposed betweenthe projection optical system and the substrate. It is also preferablethat the degassing unit determines a degassing level so that the bubbleis not generated by any change in pressure exerted on the liquid betweenthe projection optical system and the substrate.

In the present invention, it is preferable that the degassing unit is amembrane degassing unit. It is preferable that the membrane degassingunit includes a hollow fiber member. The hollow fiber member may begas-permeable and liquid-impermeable. Further, it is preferable that theliquid supply unit comprises a heating unit which heats the liquid whichis to be supplied to the membrane degassing unit to decrease aconcentration of dissolved gas in the liquid which is to be supplied tothe membrane degassing unit.

In the exposure apparatus of the present invention, it is preferablethat the liquid, for which the generation of the bubble has beensuppressed by the bubble-suppressing unit, is supplied to the spacebetween the projection optical system and the substrate without making acontact with gas.

In the exposure apparatus of the present invention, it is preferablethat the liquid supply unit includes a filter unit which filters theliquid which is to be supplied to the space between the projectionoptical system and the substrate. It is preferable that the liquidsupply unit further includes a temperature-adjusting unit which adjustsa temperature of the liquid having been degassed by the degassing unit.

In the exposure apparatus of the present invention, it is preferablethat the liquid supply unit further includes a temperature-adjustingunit which adjusts a temperature of the liquid having been degassed bythe degassing unit.

According to another aspect of the present invention, there is provideda method for producing a device, comprising using the exposure apparatusas defined in the first or second aspect of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic arrangement illustrating an embodiment of theexposure apparatus of the present invention.

FIG. 2 shows a positional relationship among a tip section of aprojection optical system, a liquid supply unit, and a liquid recoveryunit.

FIG. 3 shows an exemplary arrangement of supply nozzles and recoverynozzles.

FIG. 4 shows a schematic arrangement illustrating an embodiment of theliquid supply unit.

FIG. 5 shows a schematic arrangement illustrating another embodiment ofthe liquid supply unit.

FIG. 6 shows a schematic arrangement illustrating still anotherembodiment of the liquid supply unit.

FIG. 7 shows a sectional view illustrating a schematic arrangement of amembrane degassing unit.

FIG. 8 shows an exemplary arrangement of the supply nozzles and therecovery nozzles.

FIG. 9 shows a flow chart illustrating exemplary steps for producing asemiconductor device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

An explanation will be made below about the exposure apparatus and themethod for producing the device according to the present invention withreference to the drawings. FIG. 1 shows a schematic arrangementillustrating an embodiment of the exposure apparatus of the presentinvention.

First Embodiment

With reference to FIG. 1, an exposure apparatus EX comprises a maskstage MST which supports a mask M, a substrate stage PST which supportsa substrate P, an illumination optical system IL which illuminates, withan exposure light beam EL, the mask M supported by the mask stage MST, aprojection optical system PL which performs projection exposure for thesubstrate P supported by the substrate stage PST with an image of apattern of the mask M illuminated with the exposure light beam EL, and acontrol unit CONT which collectively controls the overall operation ofthe exposure apparatus EX.

The embodiment of the present invention will now be explained asexemplified by a case of the use of the scanning type exposure apparatus(so-called scanning stepper) as the exposure apparatus EX in which thesubstrate P is exposed with the pattern formed on the mask M whilesynchronously moving the mask M and the substrate P in mutuallydifferent directions (opposite directions) in the scanning directions.In the following explanation, the Z axis direction is the directionwhich is coincident with the optical axis AX of the projection opticalsystem PL, the X axis direction is the synchronous movement direction(scanning direction) for the mask M and the substrate P in the planeperpendicular to the Z axis direction, and the Y axis direction is thedirection (non-scanning direction) perpendicular to the Z axis directionand the Y axis direction. The directions about the X axis, the Y axis,and the Z axis are designated as θX, θY, and θZ directions respectively.The term “substrate” referred to herein includes those obtained byapplying a resist on a semiconductor wafer, and the term “mask” includesa reticle formed with a device pattern to be subjected to the reductionprojection onto the substrate.

The illumination optical system IL is used so that the mask M, which issupported on the mask stage MST, is illuminated with the exposure lightbeam EL. The illumination optical system IL includes, for example, anexposure light source, an optical integrator which uniformizes theilluminance of the light flux radiated from the exposure light source, acondenser lens which collects the exposure light beam EL supplied fromthe optical integrator, a relay lens system, and a variable fielddiaphragm which sets the illumination area on the mask M illuminatedwith the exposure light beam EL to be slit-shaped. The predeterminedillumination area on the mask M is illuminated with the exposure lightbeam EL having a uniform illuminance distribution by the illuminationoptical system IL. Those usable as the exposure light beam EL radiatedfrom the illumination optical system IL include, for example, emissionlines (g-ray, h-ray, i-ray) in the ultraviolet region radiated, forexample, from a mercury lamp, far ultraviolet light beams (DUV lightbeams) such as the KrF excimer laser beam (wavelength: 248 nm), andvacuum ultraviolet light beams (VUV light beams) such as the ArF excimerlaser beam (wavelength: 193 nm) and the F₂ laser beam (wavelength: 157nm). In this embodiment, the ArF excimer laser beam is used.

The mask stage MST supports the mask M. The mask stage MST istwo-dimensionally movable in the plane perpendicular to the optical axisAX of the projection optical system PL, i.e., in the XY plane, and it isfinely rotatable in the θZ direction. The mask stage MST is driven by amask stage-driving unit MSTD such as a linear motor. The maskstage-driving unit MSTD is controlled by the control unit CONT. Theposition in the two-dimensional direction and the angle of rotation ofthe mask M on the mask stage MST are measured in real-time by a laserinterferometer. The result of the measurement is outputted to thecontrol unit CONT. The control unit CONT drives the mask stage-drivingunit MSTD on the basis of the result of the measurement obtained by thelaser interferometer to thereby position the mask M supported on themask stage MST.

The projection optical system PL projects the pattern on the mask M ontothe substrate P at a predetermined projection magnification β to performthe exposure. The projection optical system PL includes a plurality ofoptical elements (lenses). The optical elements are supported by abarrel PK as a metal member. In this embodiment, the projection opticalsystem PL is a reduction system having the projection magnification βwhich is, for example, ¼ or ⅕. The projection optical system PL may beany one of the 1× magnification system and the magnifying system. Theoptical element (lens) 60 is exposed from the barrel PK on the side ofthe tip (on the side of the substrate P) of the projection opticalsystem PL of this embodiment. The optical element 60 is provideddetachably (exchangeably) with respect to the barrel PK.

The substrate stage PST supports the substrate P. The substrate stagePST includes a Z stage 51 which holds the substrate P by the aid of asubstrate holder, an XY stage 52 which supports the Z stage 51, and abase 53 which supports the XY stage 52. The substrate stage PST isdriven by a substrate stage-driving unit PSTD such as a linear motor.The substrate stage-driving unit PSTD is controlled by the control unitCONT. When the Z stage 51 is driven, the substrate P, which is held onthe Z stage 51, is subjected to the control of the position (focusposition) in the Z axis direction and the positions in the θX and θYdirections. When the XY stage 52 is driven, the substrate P is subjectedto the control of the position in the XY directions (position in thedirections substantially parallel to the image plane of the projectionoptical system PL). That is, the Z stage 51 controls the focus positionand the angle of inclination of the substrate P so that the surface ofthe substrate P is adjusted to match the image plane of the projectionoptical system PL in the auto-focus manner and the auto-leveling manner.The XY stage 52 positions the substrate P in the X axis direction andthe Y axis direction. It goes without saying that the Z stage and the XYstage may be provided as an integrated body.

A movement mirror 54, which is movable together with the substrate stagePST with respect to the projection optical system PL, is provided on thesubstrate stage PST (Z stage 51). A laser interferometer 55 is providedat a position opposed to the movement mirror 54. The angle of rotationand the position in the two-dimensional direction of the substrate P onthe substrate stage PST are measured in real-time by the laserinterferometer 55. The result of the measurement is outputted to thecontrol unit CONT. The control unit CONT drives the substratestage-driving unit PSTD on the basis of the result of the measurement ofthe laser interferometer 55 to thereby position the substrate Psupported on the substrate stage PST.

In this embodiment, the liquid immersion method is applied in order thatthe resolution is improved by substantially shortening the exposurewavelength and the depth of focus is substantially widened. Therefore,the space between the surface of the substrate P and the tip surface(lower surface) 7 of the optical element (lens) 60 of the projectionoptical system PL on the side of the substrate P is filled with thepredetermined liquid 50 at least during the period in which the image ofthe pattern on the mask M is transferred onto the substrate P. Asdescribed above, the lens 60 is exposed on the tip side of theprojection optical system PL, and the liquid 50 is supplied to makecontact only with the lens 60 by supply nozzles as described later on.Accordingly, the barrel PK composed of the metal is prevented from anycorrosion or the like. In this embodiment, pure water is used for theliquid 50. The exposure light beam EL, which is not limited only to theArF excimer laser beam, can be transmitted through pure water, even whenthe exposure light beam EL is, for example, the emission line (g-ray,h-ray, i-ray) in the ultraviolet region radiated, for example, from amercury lamp or the far ultraviolet light beam (DUV light beam) such asthe KrF excimer laser beam (wavelength: 248 nm).

The exposure apparatus EX includes a liquid supply unit 1 which suppliesthe predetermined liquid 50 to a space 56 between the substrate P andthe tip surface (end surface of the lens 60) 7 of the projection opticalsystem PL, and a liquid recovery unit 2 which recovers the liquid 50from the space 56. The liquid supply unit 1 is provided to fill at leasta part of the space between the projection optical system PL and thesubstrate P with the liquid 50. The liquid supply unit 1 includes, forexample, a tank for accommodating the liquid 50, and a pressurizingpump. One end of a supply tube 3 is connected to the liquid supply unit1. Supply nozzles 4 are connected to the other end of the supply tube 3.The liquid supply unit 1 supplies the liquid 50 to the space 56 throughthe supply tube 3 and the supply nozzles 4.

The liquid recovery unit 2 includes, for example, a suction pump, and atank for accommodating the recovered liquid 50. One end of a recoverytube 6 is connected to the liquid recovery unit 2. Recovery nozzles 5are connected to the other end of the recovery tube 6. The liquidrecovery unit 2 recovers the liquid 50 from the space 56 through therecovery nozzles 5 and the recovery tube 6. When the space 56 is filledwith the liquid 50, then the control unit CONT drives the liquid supplyunit 1 so that the liquid 50, which is in a predetermined amount perunit time, is supplied to the space 56 through the supply tube 3 and thesupply nozzles 4, and the control unit CONT drives the liquid recoveryunit 2 so that the liquid 50, which is in a predetermined amount perunit time, is recovered from the space 56 through the recovery nozzles 5and the recovery tube 6. Accordingly, the liquid 50 is retained in thespace 56 between the substrate P and the tip surface 7 of the projectionoptical system PL.

FIG. 2 shows a partial magnified view of FIG. 1 illustrating, forexample, the lower portion of the projection optical system PL of theexposure apparatus EX, the liquid supply unit 1, and the liquid recoveryunit 2. In FIG. 2, the lens 60, which is disposed at the lowest end ofthe projection optical system PL has an end portion 60A which is formedso that the end portion 60A has a rectangular shape which is long in theY axis direction (non-scanning direction) and which has necessaryportion in the scanning direction. During the scanning exposure, apattern image of a part of the mask M is projected onto the rectangularprojection area disposed just under the end portion 60A. The mask M ismoved at the velocity V in the −X direction (or in the +X direction)with respect to the projection optical system PL, in synchronizationwith which the substrate P is moved at the velocity β·V (β is theprojection magnification) in the +X direction (or in the −X direction)by the aid of the XY stage 52. After the completion of the exposure forone shot area, the next shot area is moved to the scanning startposition in accordance with the stepping of the substrate P. Theexposure process is successively performed thereafter for each of theshot areas in accordance with the step-and-scan system. This embodimentis designed so that the liquid 50 is allowed to flow in the samedirection as the movement direction of the substrate P in parallel tothe movement direction of the substrate P.

FIG. 3 shows the positional relationship among the end portion 60A ofthe lens 60 of the projection optical system PL, the supply nozzles 4(4A to 4C) for supplying the liquid 50 in the X axis direction, and therecovery nozzles 5 (5A, 5B) for recovering the liquid 50. In FIG. 3, theend portion 60A of the lens 60 has a rectangular shape which is long inthe Y axis direction. The three supply nozzles 4A to 4C are arranged onthe side in the +X direction, and the two recovery nozzles 5A, 5B arearranged on the side in the −X direction so that the end portion 60A ofthe lens 60 of the projection optical system PL is interposedtherebetween in the X axis direction. The supply nozzles 4A to 4C areconnected to the liquid supply unit 1 through the supply tube 3, and therecovery nozzles 5A, 5B are connected to the liquid recovery unit 2through the recovery tube 4. Further, the supply nozzles 8A to 8C andthe recovery nozzles 9A, 9B are arranged at positions obtained byrotating, by substantially 180°, the positions of the supply nozzles 4Ato 4C and the recovery nozzles 5A, 5B about the center of the endportion 60A. The supply nozzles 4A to 4C and the recovery nozzles 9A, 9Bare alternately arranged in the Y axis direction. The supply nozzles 8Ato 8C and the recovery nozzles 5A, 5B are alternately arranged in the Yaxis direction. The supply nozzles 8A to 8C are connected to the liquidsupply unit 1 through the supply tube 10. The recovery nozzles 9A, 9Bare connected to the liquid recovery unit 2 through the recovery tube11. The liquid is supplied from the nozzles so that no gas portion isgenerated between the projection optical system PL and the substrate P.

FIG. 4 shows an arrangement of the liquid supply unit 1. As shown inFIG. 4, the liquid supply unit 1 includes a degassing unit 21 as abubble-suppressing unit which suppresses the generation of the bubble inthe liquid 50. The degassing unit 21 shown in FIG. 4 includes a heatingunit which heats the liquid 50. In this embodiment, the liquid 50 iscirculated between the liquid supply unit 1 and the liquid recovery unit2. The liquid 50, which is supplied from the liquid recovery unit 2, isreturned to the liquid supply unit 1 through a circulating tube 12. Apressurizing pump 15, which feeds the liquid toward the upstream side,is provided for the liquid supply unit 1.

The liquid supply unit 1 includes a filter 20 which removes any foreignmatter or the like from the liquid 50 recovered by the liquid recoveryunit 2, for example, by filtering the liquid 50 recovered by the liquidrecovery unit 2 in order to avoid any pollution of the substrate P andthe projection optical system PL and/or avoid any deterioration of thepattern image projected onto the substrate P, the heating unit 21 whichheats the liquid 50 having passed through the filter 20 to apredetermined temperature (for example, 90° C.), and atemperature-adjusting unit 22 which adjusts the temperature of theliquid 50 having been heated by the heating unit 21 to a desiredtemperature. Although not shown in FIG. 4, the liquid supply unit 1includes a reservoir such as a tank capable of retaining a predeterminedamount of the liquid 50. In this embodiment, the temperature-adjustingunit 22, which is provided for the liquid supply unit 1, sets thetemperature of the liquid 50 to be supplied to the space 56 to beapproximately equivalent, for example, to the temperature (for example,23° C.) in the chamber in which the exposure apparatus EX isaccommodated. Supply tubes 3, 10 are connected to thetemperature-adjusting unit 22. The liquid 50, which has beentemperature-adjusted by the temperature-adjusting unit 22, is suppliedto the space 56 through the supply tube 3 (10).

As for the heating unit 21, for example, the liquid 50 is accommodatedin an accommodating unit such as a tank, and the liquid 50 is heated byheating the accommodating unit. A discharge tube 13, which constitutes apart of a discharge unit, is connected to the accommodating unit. Theoperation of the heating unit 21 is controlled by the control unit CONT.The heating unit 21 heats the liquid 50 to a predetermined temperature,and thus the gas, which is dissolved in the liquid 50, is removed(degassed) from the liquid 50. The extracted gas component is dischargedthrough the discharge tube 13 to the outside of the apparatus. Theliquid 50 is degassed by the heating unit 21, and thus the generation ofthe bubble is suppressed. For example, the following technique may beadopted for the heating unit 21. That is, an electric heater is woundaround the outer circumference of a stainless steel reservoir capable ofretaining the liquid 50, and the temperature of the electric heater iscontrolled. Alternatively, a helical tube made of stainless steel isimmersed in a temperature-controlled high temperature liquid, and theliquid 50 is allowed to flow through the helical tube.

In this embodiment, the heating unit 21 sets the temperature of theliquid 50 to be not less than 30° C. and not more than 100° C. That is,the liquid 50 is heated at a temperature higher than the temperature(for example, 23° C. as the temperature in the chamber) set by thetemperature-adjusting unit 22, and within a temperature range of notmore than the boiling point of the liquid. The heating unit 21 degassesthe liquid 50 by heating the liquid 50 within the temperature range asdescribed above to suppress the generation of the bubble in the liquid50 to be supplied to the space 56. In particular, the heating unit 21can sufficiently degas the liquid 50 by heating the liquid 50 to theboiling point thereof.

It is preferable that the liquid 50 is set by the heating unit 21 tohave a temperature which is higher than the temperature in the chamber(space 56) and which is not more than the boiling point. Therefore, whenthe liquid 50 is a liquid other than water, the heating unit 21 heatsthe liquid depending on the boiling point of the liquid.

Next, an explanation will be made about a procedure for exposing thesubstrate P with the pattern of the mask M by using the exposureapparatus EX described above.

When the mask M is loaded on the mask stage MST, and the substrate P isloaded on the substrate stage PST, then the control unit CONT drives theliquid supply unit 1 to start the operation for supplying the liquid tothe space 56. The liquid 50 passes through the filter 20 in the liquidsupply unit 1, and thus the liquid 50 is supplied to the heating unit 21in a state in which any foreign matter or the like is removed therefrom.The liquid 50, which is supplied to the heating unit 21, is heated to apredetermined temperature. The liquid 50 is degassed by being heated tothe predetermined temperature by the heating unit 21. The removed gascomponent is discharged to the outside of the apparatus through thedischarge tube 13 which constitutes a part of the discharge unit. Thedegassed liquid 50 is supplied to the temperature-adjusting unit 22.After the temperature is adjusted, for example, to a temperatureapproximately equal to the temperature in the chamber, the liquid 50 issupplied to the space 56 through the supply tube 3 and the supplynozzles 4. It is noted that the flow passage for the liquid 50, whichincludes, for example, the tube 14 for connecting the heating unit 21and the temperature-adjusting unit 22, the temperature-adjusting unit22, and the supply tube 3, is tightly closed and sealed. The liquid 50flows through the flow passage in a state in which the flow passage issufficiently filled with the liquid 50. That is, the liquid 50, whichflows through the flow passage, is supplied to the space 56 withoutmaking any contact with the gas. The inner wall surface (contact surfacewith the liquid), which includes those of the supply tube 3 and the likefor forming the flow passage running from the heating unit 21 to achievethe supply to the space 56, is hydrophilic. The generation of the bubblein the liquid is suppressed in the flow passage running from the heatingunit 21 to the space 56. In this case, for example, a stainless steelpipe subjected to the electrolytic polishing may be used as the supplytube 3. It is also preferable that the liquid 50 in the degassed stateis stored in a storage reservoir or a pipe without making contact withthe gas, and the liquid 50 is supplied to the space 56 at a desiredtiming. In this procedure, the flow passage, the storage reservoir, andthe pipe also function as parts of the bubble-suppressing unit, inaddition to the heating unit 21.

When the scanning exposure is performed by moving the substrate P in thescanning direction (−X direction) indicated by an arrow Xa (see FIG. 3),the liquid 50 is supplied and recovered with the liquid supply unit 1and the liquid recovery unit 2 by using the supply tube 3, the supplynozzles 4A to 4C, the recovery tube 4, and the recovery nozzles 5A, 5B.That is, when the substrate P is moved in the −X direction, then theliquid 50, for which the generation of the bubble is suppressed, issupplied to the space between the projection optical system PL and thesubstrate P from the liquid supply unit 1 through the supply tube 3 andthe supply nozzles 4 (4A to 4C), and the liquid 50 is recovered to theliquid recovery unit 2 through the recovery nozzles 5 (5A, 5B) and therecovery tube 6. The liquid 50 flows in the −X direction so that thespace between the lens 60 and the substrate P is filled therewith. Onthe other hand, when the scanning exposure is performed by moving thesubstrate P in the scanning direction (+X direction) indicated by anarrow Xb, then the liquid 50 is supplied and recovered with the liquidsupply unit 1 and the liquid recovery unit 2 by using the supply tube10, the supply nozzles 8A to 8C, the recovery tube 11, and the recoverynozzles 9A, 9B. That is, when the substrate P is moved in the +Xdirection, then the degassed liquid 50 is supplied from the liquidsupply unit 1 to the space between the projection optical system PL andthe substrate P through the supply tube 10 and the supply nozzles 8 (8Ato 8C), and the liquid 50 is recovered to the liquid recovery unit 2through the recovery nozzles 9 (9A, 9B) and the recovery tube 11. Theliquid 50 flows in the +X direction so that the space between the lens60 and the substrate P is filled therewith. As described above, thecontrol unit CONT allows the liquid 50 to flow in the movement directionof the substrate P by using the liquid supply unit 1 and the liquidrecovery unit 2. In this arrangement, for example, the liquid 50, whichis supplied from the liquid supply unit 1 through the supply nozzles 4,flows so that the liquid 50 is attracted and introduced into the space56 in accordance with the movement of the substrate P in the −Xdirection. Therefore, even when the supply energy of the liquid supplyunit 1 is small, the liquid 50 can be supplied to the space 56 withease. When the direction, in which the liquid 50 is allowed to flow, isswitched depending on the scanning direction, then it is possible tofill the space between the substrate P and the tip surface 7 of the lens60 with the liquid 50, and it is possible to obtain the high resolutionand the wide depth of focus, even when the substrate P is subjected tothe scanning in any one of the +X direction and the −X direction.

As explained above, the heating unit 21, which heats the liquid 50, isprovided for the exposure apparatus, especially for the liquid supplyunit 1 for supplying the liquid 50 to the space between the projectionoptical system PL and the substrate P. Accordingly, the liquid 50 can besupplied to the space between the projection optical system PL and thesubstrate P, after the liquid 50 is sufficiently degassed. Therefore, itis possible to suppress the generation of the bubble in the liquid 50which fills the space between the projection optical system PL and thesubstrate P during the exposure process. Even if the bubble is generatedby any cause, for example, in the flow passage between the heating unit(degassing unit) 21 and the space 56, on the tip surface 7 of theprojection optical system PL, or on the surface of the substrate P, thenthe liquid 50, which is sufficiently degassed, flows through the flowpassage and the space 56, and thus the liquid 50 can absorb and removethe bubble existing in the flow passage. The liquid 50, which issupplied to the space 56 between the projection optical system PL andthe substrate P, makes contact with the gas (air) existing therearound.Therefore, it is feared that the gas (air) existing therearound may bedissolved in the liquid 50. However, it takes about several minutes todissolve the gas (air) in the liquid 50. Therefore, the liquid 50, whichis supplied from the liquid supply unit 1, is recovered by the liquidrecovery unit 2, before the liquid 50 loses the degassed property.Therefore, no bubble is generated as well in the liquid 50 between theprojection optical system PL and the substrate P by the dissolution ofthe gas (air) in the liquid 50 in the space 56. As described above, theexposure process can be performed in the state in which no bubble existsin the liquid 50 on the optical path for the exposure light beam EL.Therefore, it is possible to avoid the deterioration of the patternimage which would be otherwise caused by the bubble, and it is possibleto produce a device having a high pattern accuracy. It is also allowablethat the heating unit 21 is not provided in the liquid supply unit 1.The heating unit 21 may be provided at a place separated from the liquidsupply unit 1, or the heating unit 21 may be provided inside or outsidethe chamber of the exposure apparatus.

The liquid 50 is supplied to the space in the state in which thetemperature is adjusted by the temperature-adjusting unit 22. Therefore,the temperature is adjusted for the surface of the substrate P. It ispossible to avoid the deterioration of, for example, the alignmentaccuracy, which would be otherwise caused by the thermal expansion ofthe substrate P due to the heat generated during the exposure.

As described above, pure water is used as the liquid 50 in thisembodiment. Pure water is advantageous in that pure water is availablein a large amount with ease, for example, in the semiconductorproduction factory, and pure water exerts no harmful influence, forexample, on the optical element (lens) and the photoresist on thesubstrate P. Further, pure water exerts no harmful influence on theenvironment, and the content of impurity is extremely low. Therefore, itis also expected to obtain the function to wash the surface of thesubstrate P and the surface of the optical element provided at the tipsurface of the projection optical system PL.

It is approved that the refractive index n of pure water (water) withrespect to the exposure light beam EL having a wavelength of about 193nm is approximately in an extent of 1.44 to 1.47. When the ArF excimerlaser beam (wavelength: 193 nm) is used as the light source of theexposure light beam EL, then the wavelength is shortened on thesubstrate P by 1/n, i.e., to about 131 to 134 nm, and a high resolutionis obtained. Further, the depth of focus is magnified about n times,i.e., about 1.44 to 1.47 times as compared with the value obtained inthe air. Therefore, when it is enough to secure an approximatelyequivalent depth of focus as compared with the case of the use in theair, it is possible to further increase the numerical aperture of theprojection optical system PL. Also in this viewpoint, the resolution isimproved.

In this embodiment, the lens 60 is attached to the tip of the projectionoptical system PL. However, the optical element, which is attached tothe tip of the projection optical system PL, may be an optical platewhich is usable to adjust the optical characteristics of the projectionoptical system PL, for example, the aberration (for example, sphericalaberration and comatic aberration). Alternatively, the optical elementmay be a parallel plane plate through which the exposure light beam ELis transmissive. When the optical element, which makes contact with theliquid 50, is the parallel plane plate which is cheaper than the lens,it is enough that the parallel plane plate is merely exchangedimmediately before supplying the liquid 50 even when any substance (forexample, any silicon-based organic matter), which deteriorates thetransmittance of the projection optical system PL, the illuminance ofthe exposure light beam EL on the substrate P, and the uniformity of theilluminance distribution, is adhered to the parallel plane plate, forexample, during the transport, the assembling, and/or the adjustment ofthe exposure apparatus EX. An advantage is obtained such that theexchange cost is lowered as compared with the case in which the opticalelement to make contact with the liquid 50 is the lens. That is, thesurface of the optical element to make contact with the liquid 50 isdirtied, for example, due to the adhesion of scattered particlesgenerated from the resist by being irradiated with the exposure lightbeam EL or any impurity contained in the liquid 50. Therefore, it isnecessary to periodically exchange the optical element. However, whenthe optical element is the cheap parallel plane plate, then the cost ofthe exchange part is low as compared with the lens, and it is possibleto shorten the time required for the exchange. Thus, it is possible tosuppress the increase in the maintenance cost (running cost) and thedecrease in the throughput.

When the pressure, which is generated by the flow of the liquid 50, islarge between the substrate P and the optical element disposed at thetip of the projection optical system PL, it is also allowable that theoptical element is tightly fixed so that the optical element is notmoved by the pressure, rather than allowing the optical element to beexchangeable.

This embodiment is constructed such that the space between theprojection optical system PL and the surface of the substrate P isfilled with the liquid 50. However, for example, the space may be filledwith the liquid 50 in a state in which a cover glass composed of aparallel flat plate is attached to the surface of the substrate P.

The liquid 50 is water in this embodiment. However, the liquid 50 may beany liquid other than water. For example, when the light source of theexposure light beam EL is the F₂ laser, the F₂ laser beam is nottransmitted through water. Therefore, in this case, for example, it isalso allowable to use, as the liquid 50, fluorine-based oil(fluorine-based liquid) and perfluoropolyether (PFPE) through which theF₂ laser beam is transmissive. Alternatively, other than the above, itis also possible to use, as the liquid 50, those (for example, cedaroil) which have the transmittance with respect to the exposure lightbeam EL, which have the refractive index as high as possible, and whichare stable against the photoresist applied to the surface of thesubstrate P and the projection optical system PL.

Second Embodiment

Next, an explanation will be made with reference to FIG. 5 about asecond embodiment of the exposure apparatus EX of the present invention.In the following description, the same or equivalent constitutive partsas those of the embodiment described above are designated by the samereference numerals, any explanation of which is simplified or omitted.The characteristic feature of this embodiment is that apressure-reducing unit 23 is provided in place of the heating unit 21.

As shown in FIG. 5, the liquid supply unit 1 includes a filter 20 whichremoves any foreign matter from the liquid 50, for example, by filteringthe liquid 50 recovered by the liquid recovery unit 2 in order to avoidany pollution of the substrate P and the projection optical system PLand/or avoid any deterioration of the pattern image projected onto thesubstrate P, the pressure-reducing unit 23 which degasses the liquid 50by reducing the pressure of the liquid 50 from which the foreign matterhas been removed by the filter 20, a temperature-adjusting unit 22 whichadjusts the temperature of the liquid 50 having been subjected to thedegassing treatment by the pressure-reducing unit 23 to a temperatureapproximately identical to the temperature in the chamber, and apressurizing pump 15. The pressure-reducing unit 23 includes a reservoirwhich retains the liquid 50. The liquid 50 is degassed by reducing thepressure in the reservoir. The liquid 50 can be also degassed byreducing the pressure rather than by heating the liquid 50 as describedabove. The pressure-reducing unit 50 may include, for example, areservoir which is capable of retaining a predetermined amount of theliquid 50, and a vacuum pump which is connected to the reservoir andwhich reduces the pressure of the gas that makes contact with the liquid50 in the reservoir.

The heating treatment and the pressure-reducing treatment may beperformed simultaneously for the liquid 50 in order to degas the liquid50. That is, the pressure-reducing unit 23, which has the reservoircapable of retaining the liquid 50, may be provided with a heating unitfor heating the reservoir. The pressure-reducing unit 23 can degas theliquid 50 by accommodating the liquid 50 in the reservoir and heatingthe liquid 50 by using the heating unit while reducing the pressure inthe reservoir.

In this procedure, the pressure-reducing unit 23 sets the pressuredepending on the temperature of the liquid 50. That is, a sufficientdegassing effect is obtained by heating the liquid 50 to the boilingpoint. However, the boiling point of the liquid 50 depends on thepressure. Therefore, the liquid 50 can be degassed efficiently andsatisfactorily by setting the pressure depending on the temperature ofthe liquid 50. For example, the pressure (boiling pressure), at whichthe boiling point of water as the liquid 50 is 100° C., is theatmospheric pressure (101,325 Pa). The boiling pressure, at which theboiling point is 90° C., is 70,121 Pa. Similarly, the boiling pressureis 47,377 Pa at a boiling point of 80° C., the boiling pressure is12,345 Pa at a boiling point of 50° C., the boiling pressure is 4,244.9Pa at a boiling point of 30° C., and the boiling pressure is 2,338.1 Paat a boiling point of 20° C. Therefore, for example, when thetemperature of the liquid 50 is set to 100° C. by the heating unit, thepressure-reducing unit 23 can degas the liquid 50 by boiling the liquid50 at the atmospheric pressure without performing the pressure-reducingtreatment. On the other hand, when the temperature of the liquid 50 is90° C., the pressure-reducing unit 23 can degas the liquid 50 by boilingthe liquid 50 by setting the pressure to be within a range from theatmospheric pressure to the boiling pressure (70,121 Pa) at thetemperature of 90° C. Similarly, for example, when the temperature ofthe liquid 50 is 30° C., the pressure-reducing unit 23 can degas theliquid 50 by boiling the liquid 50 by setting the pressure to be withina range from the atmospheric pressure to the boiling pressure (4,244.9Pa). As described above, the boiling point of the liquid 50 variesdepending on the pressure. Therefore, the pressure-reducing unit 23 candegas the liquid 50 satisfactorily by setting the pressure depending onthe temperature of the liquid 50.

The degassing level of the liquid 50 to be supplied to the space betweenthe projection optical system PL and the substrate P, i.e., theconcentration of dissolved gas of the liquid 50 may be determineddepending on the condition of use of the liquid 50 (for example, theexposure condition). In the case of the liquid immersion exposure, thetemperature of the liquid 50 disposed between the projection opticalsystem PL and the substrate P is entirely or partially raised during theexposure due to the radiation of the exposure light beam EL or the heatof the substrate P heated by the radiation of the exposure light beamEL. The increase in the temperature of the liquid 50 differs, forexample, depending on the intensity of the exposure light beam EL, whichis about several degrees (1 to 3° C.). However, if the degassing levelof the liquid 50 is low, there is such a possibility that the gas, whichhas been dissolved in the liquid 50, may be converted into the generatedbubble due to the increase in the temperature of the liquid 50.Therefore, it is necessary to set the degassing level of the liquid 50so that the bubble is not generated even when the increase in thetemperature arises in the liquid 50 between the projection opticalsystem PL and the substrate P. For example, as described above, when theliquid, which is temperature-controlled to about 23° C., is supplied tothe space between the projection optical system PL and the substrate P,the degassing level may be set so that the bubble is not generated, forexample, even when the temperature of the liquid is raised to 30° C., inview of the safety. Specifically, the degassing level of the liquid 50,i.e., of water may be set to be not more than the saturation amount ofair dissolved in water at 30° C., i.e., 0.016 cm³/cm³ (not more than 13ppm for N₂ and not more than 7.8 ppm for O₂ as expressed by the massratio). The expression “cm³/cm³” indicates the volume cm³ of airdissolved in 1 cm³ of water.

In the case of the liquid immersion exposure, when the flow appears inthe liquid 50 between the projection optical system PL and the substrateP, the pressure change arises in the liquid 50. The pressure changediffers depending on, for example, the supply amount of the liquid, therecovery amount of the liquid, and the movement speed of the substrateP, which is about several hundreds Pa (100 to 300 Pa). However, if thedegassing level of the liquid 50 is low, there is such a possibilitythat the bubble may be generated in the liquid 50 due to the pressurechange in relation to the liquid 50. Therefore, the degassing level ofthe liquid 50 may be set so that the bubble is not generated by thepressure change of several hundreds Pa of the liquid 50.

When it is difficult to raise the degassing level, it is also allowablethat the exposure condition is determined so that the temperature changeand the pressure change, which may generate the bubble, do not occur inthe liquid between the projection optical system PL and the substrate P.The exposure condition includes at least one of the supply amount of theliquid, the recovery amount of the liquid, the movement speed of thesubstrate P, the exposure light beam intensity, the emission cycle ofthe exposure pulse light beam (pulse interval), and the pulse width ofthe exposure pulse light beam. It goes without saying that it isnecessary to determine the exposure condition in view of the preventionof the occurrence of the bubble as well as the prevention of thedeterioration of the image formation of the pattern image resulting fromthe change in the refractive index of the liquid, when the exposurecondition is determined in consideration of the temperature change andthe pressure change of the liquid.

Third Embodiment

An explanation will be made with reference to FIGS. 6 and 7 about athird embodiment of the exposure apparatus EX of the present invention.The exposure apparatus of this embodiment is provided with a membranedegassing unit 24 and a heating unit 25 as shown in FIG. 6 in place ofthe heating unit of the liquid supply unit in the first embodiment. Inthe following description, the same or equivalent constitutive parts asthose of the embodiment described above are designated by the samereference numerals, any explanation of which is simplified or omitted.

FIG. 6 shows an arrangement of the liquid supply unit 1. As shown inFIG. 6, the liquid supply unit 1 includes a filter 20 which removes anyforeign matter or the like from the liquid 50 recovered by the liquidrecovery unit 2, for example, by filtering the liquid 50 recovered bythe liquid recovery unit 2 in order to avoid any pollution of thesubstrate P and the projection optical system PL and/or avoid anydeterioration of the pattern image projected onto the substrate P, theheating unit 25 which heats the liquid 50 having passed through thefilter 20 to a predetermined temperature, the membrane degassing unit 24which removes the gas from the liquid 50 heated by the heating unit 25,a temperature-adjusting unit 22 which adjusts the temperature of theliquid 50 having been subjected to the degassing treatment by themembrane degassing unit 24 to be a desired temperature, and apressurizing pump 15. The liquid 50, for which the concentration ofdissolved gas has been lowered by the heating unit 25, is supplied tothe membrane degassing unit 24 through the tube 12. The liquid 50, whichhas been degassed by the membrane degassing unit 24, is supplied to thetemperature-adjusting unit 22 through the tube 14. The membranedegassing unit 24 is connected to the discharge tube 13 to discharge thegas removed (degassed) from the liquid 50. The temperature-adjustingunit 22 sets the temperature of the liquid 50 to be supplied to thespace 56 to be approximately equivalent, for example, to the temperature(for example, 23° C.) in the chamber in which the exposure apparatus EXis accommodated. Supply tubes 3, 10 are connected to thetemperature-adjusting unit 22. The liquid 50, which has beentemperature-adjusted by the temperature-adjusting unit 22, is suppliedto the space 56 through the supply tube 3 (10) by the pressurizing pump15. The operation of the membrane degassing unit 24 is also controlledby the control unit CONT.

FIG. 7 shows a sectional view illustrating a schematic arrangement ofthe membrane degassing unit 24. A cylindrical hollow fiber bundle 72 isaccommodated in a housing 71 while leaving a predetermined space 73. Thehollow fiber bundle 72 includes a plurality of straw-shaped hollow fibermembranes 74 which are bundled in parallel. Each of the hollow fibermembranes 74 is formed of a material (for example,poly-4-methylpentene-1) which is highly hydrophobic and which isexcellent in gas permeability. Vacuum cap members 75 a, 75 b are fixedat the both ends of the housing 71. Tightly sealed spaces 76 a, 76 b areformed at the outside of the housing 71 at the both ends. Degassingports 77 a, 77 b, which are connected to an unillustrated vacuum pump,are provided for the vacuum cap members 75 a, 75 b. Sealing sections 78a, 78 b are formed at the both ends of the housing 71 so that only theboth ends of the hollow fiber bundle 72 are connected to the tightlysealed spaces 76 a, 76 b, respectively. The vacuum pump, which isconnected to the degassing ports 77 a, 77 b, can be used to provide thepressure-reduced state for the inside of each of the hollow fibermembranes 74. A tube 79, which is connected to the tube 12, is arrangedin the hollow fiber bundle 72. The tube 79 is provided with a pluralityof liquid supply holes 80. The liquid 50 is supplied from the liquidsupply holes 80 to a space 81 which is surrounded by the sealingsections 78 a, 78 b and the hollow fiber bundle 72. When the liquid 50is continuously supplied from the liquid supply holes 80 to the space81, then the liquid 50 flows toward the outside so that the liquid 50traverses the layers of the hollow fiber membranes 74 bundled inparallel, and the liquid 50 makes contact with the outer surfaces of thehollow fiber membranes 74. As described above, each of the hollow fibermembranes 74 is formed of the material which is highly hydrophobic andwhich is excellent in gas permeability. Therefore, the liquid 50 doesnot enter the inside of the hollow fiber membrane 74, and the liquid 50passes through interstices of the respective hollow fiber membranes 74to move to the space 73 disposed outside the hollow fiber bundle 72. Onthe other hand, the gas (molecule) dissolved in the liquid 50 is moved(absorbed) to the inside of each of the hollow fiber membranes 74,because the inside of each of the hollow fiber membranes 74 is in apressure-reduced state (about 20 Torr). The gas component, which isremoved (degassed) from the liquid 50 during the traverse across thelayers of the hollow fiber membranes 74 as described above, passesthrough the both ends of the hollow fiber bundle 72, and the gascomponent is discharged from the degassing ports 77 a, 77 b via thetightly sealed spaces 76 a, 76 b as shown by arrows 83. The liquid 50,which has been subjected to the degassing treatment, is supplied to thetemperature-adjusting unit 22 through the tube 14 from a liquid outlet82 provided for the housing 51.

As explained above, the liquid supply unit 1, which supplies the liquid50 to the space between the projection optical system PL and thesubstrate P, is provided with the membrane degassing unit 24 whichremoves (degasses) the gas from the liquid 50. Accordingly, the liquid50 can be supplied to the space between the projection optical system PLand the substrate P after the liquid 50 is sufficiently degassed.Therefore, it is possible to suppress the generation of the bubble inthe liquid 50 which fills the space between the projection opticalsystem PL and the substrate P during the exposure process. Even if thebubble is generated by any cause, for example, in the flow passagebetween the membrane degassing unit 24 and the space 56, on the tipsurface 7 of the projection optical system PL, or on the surface of thesubstrate P, then the sufficiently degassed liquid 50 flows through theflow passage and the space 56, and thus the liquid 50 can absorb andremove the bubble existing in the flow passage. As described above, theexposure process can be performed in the state in which no bubble ispresent in the liquid 50 on the optical path for the exposure light beamEL. Therefore, it is possible to avoid the deterioration of the patternimage which would be otherwise caused by the bubble, and it is possibleto produce a device having a high pattern accuracy.

In this embodiment, the liquid is heated by the heating unit 25 to lowerthe concentration of dissolved gas, and then the liquid is supplied tothe membrane degassing unit 24. Thus, the degassing level is improvedfor the liquid to be supplied to the space 56. However, apressure-reducing unit may be used in place of the heating unit 25 tolower the concentration of dissolved gas, and then the liquid may besupplied to the membrane degassing unit 24. When the degassing abilityof the membrane degassing unit 24 is sufficiently high, the liquid,which has passed through the filter 20, may be introduced into themembrane degassing unit 24 without passing along the heating unit andthe pressure-reducing unit.

In the respective embodiments described above, the shape of the nozzleis not specifically limited. For example, two pairs of the nozzles maybe used to supply or recover the liquid 50 for the long side of the endportion 60A. In this arrangement, the supply nozzles and the recoverynozzles may be arranged while being aligned vertically in order that theliquid 50 can be supplied and recovered in any one of the directions ofthe +X direction and the −X direction.

As shown in FIG. 8, the supply nozzles 31, 32 and the recovery nozzles33, 34 may be provided on the both sides in the Y axis directionrespectively with the end portion 60A intervening therebetween. Thesupply nozzles and the recovery nozzles can be used to stably supply theliquid 50 to the space between the projection optical system PL and thesubstrate P as well during the movement of the substrate P in thenon-scanning direction (Y axis direction) when the stepping movement isperformed.

In the embodiments described above, the liquid, from which the gas hasbeen removed by the gas-removing unit (heating unit 21,pressure-reducing unit 23, membrane degassing unit 24), is supplied tothe space 56 between the projection optical system PL and the substrateP without making any contact with the gas. However, if it is confirmedthat the gas is sufficiently removed, and the amount of the gasdissolved in the liquid is small, then the liquid may make contact withthe gas in a part of or all of the flow passage. That is, thearrangement, in which the liquid is intended to make no contact with thegas between the gas-removing unit and the space 56, is not essential tosuppress the gas.

In the embodiments described above, the mechanism is constructed suchthat the liquid, which is recovered by the liquid recovery unit 2, isreturned to the liquid supply unit 1. However, such a mechanism is notnecessarily indispensable. It is also allowable that fresh or new purewater is fed to the liquid supply unit 1, and the liquid, which isrecovered by the liquid recovery unit 2, is discarded.

In the embodiments described above, the explanation has been made aboutthe case in which the liquid immersion area is formed on the side of theimage plane of the projection optical system PL when the substrate P issubjected to the exposure. However, the present invention is not limitedonly to the case in which the substrate P is subjected to the exposure.In some cases, the liquid is arranged on the side of the image plane ofthe projection optical system PL to perform various measurements throughthe liquid as well when various measuring members and measuring sensorsprovided on the substrate stage PST (Z stage 51) are used. Even when themeasurement as described above is performed, it is possible to avoid,for example, any measurement error caused by the bubble, by suppressingthe generation of the bubble in the liquid in the same manner asdescribed above.

In the embodiments described above, the liquid supply unit and theliquid recovery unit are constructed such that the supply nozzles andthe recovery nozzles are provided on the both sides of the projectionarea of the projection optical system PL, the liquid is supplied fromone side of the projection area and the liquid is recovered on the otherside depending on the scanning direction of the substrate P. However,the arrangement of the liquid supply unit and the liquid recovery unitis not limited thereto. It is enough that the liquid can be locallyretained between the projection optical system PL and the substrate P.

The substrate P, which is usable in the respective embodiments describedabove, is not limited to the semiconductor wafer for producing thesemiconductor device. Those applicable include, for example, the glasssubstrate for the display device, the ceramic wafer for the thin filmmagnetic head, and the master plate (synthetic quartz, silicon wafer)for the mask or the reticle to be used for the exposure apparatus.

In the embodiments described above, the exposure apparatus is adopted,in which the space between the projection optical system PL and thesubstrate P is locally filled with the liquid. However, the presentinvention is also applicable to a liquid immersion exposure apparatus inwhich a stage holding a substrate as an exposure objective is moved in aliquid bath, and a liquid immersion exposure apparatus in which a liquidpool having a predetermined depth is formed on a stage and a substrateis held therein. The structure and the exposure operation of the liquidimmersion exposure apparatus in which the stage holding the substrate asthe exposure objective is moved in the liquid bath are described indetail, for example, in Japanese Patent Application Laid-open No.6-124873, content of which is incorporated herein by reference within arange of permission of the domestic laws and ordinances of the statedesignated or selected in this international application. The structureand the exposure operation of the liquid immersion exposure apparatus inwhich the liquid pool having the predetermined depth is formed on thestage and the substrate is held therein are described in detail, forexample, in Japanese Patent Application Laid-open No. 10-303114 and U.S.Pat. No. 5,825,043, contents of which are incorporated herein byreference respectively within a range of permission of the domestic lawsand ordinances of the state designated or selected in this internationalapplication.

As for the exposure apparatus EX, the present invention is alsoapplicable to the scanning type exposure apparatus (scanning stepper)based on the step-and-scan system for performing the scanning exposurefor the pattern of the mask M by synchronously moving the mask M and thesubstrate P as well as the projection exposure apparatus (stepper) basedon the step-and-repeat system for performing the full field exposure forthe pattern of the mask M in a state in which the mask M and thesubstrate P are allowed to stand still, while successively step-movingthe substrate P. The present invention is also applicable to theexposure apparatus based on the step-and-stitch system in which at leasttwo patterns are partially overlaid and transferred on the substrate P.

The present invention is also applicable to a twin-stage type exposureapparatus. The structure and the exposure operation of the twin-stagetype exposure apparatus are disclosed, for example, in Japanese PatentApplication Laid-open Nos. 10-163099 and 10-214783 (corresponding toU.S. Pat. Nos. 6,341,007, 6,400,441, 6,549,269, and 6,590,634),Published Japanese Translation of PCT International Publication forPatent Application No. 2000-505958 (corresponding to U.S. Pat. No.5,969,441), and U.S. Pat. No. 6,208,407, contents of which areincorporated herein by reference respectively within a range ofpermission of the domestic laws and ordinances of the state designatedor selected in this international application.

As for the type of the exposure apparatus EX, the present invention isnot limited to the exposure apparatus for the semiconductor productionapparatus for exposing the substrate P with the semiconductor devicepattern. The present invention is also widely applicable, for example,to the exposure apparatus for producing the liquid crystal displaydevice or for producing the display as well as the exposure apparatusfor producing, for example, the thin film magnetic head, the imagepickup device (CCD), the reticle, or the mask.

When the linear motor is used for the substrate stage PST and/or themask stage MST, it is allowable to use any one of those of the airfloating type based on the use of the air bearing and those of themagnetic floating type based on the use of the Lorentz's force or thereactance force. Each of the stages PST, MST may be either of the typein which the movement is effected along the guide or of the guidelesstype in which no guide is provided. An example of the use of the linearmotor for the stage is disclosed in U.S. Pat. Nos. 5,623,853 and5,528,118, contents of which are incorporated herein by referencerespectively within a range of permission of the domestic laws andordinances of the state designated or selected in this internationalapplication.

As for the driving mechanism for each of the stages PST, MST, it is alsoallowable to use a plane motor in which a magnet unit provided withtwo-dimensionally arranged magnets and an armature unit provided withtwo-dimensionally arranged coils are opposed to one another, and each ofthe stages PST, MST is driven by the electromagnetic force. In thisarrangement, any one of the magnet unit and the armature unit isconnected to the stage PST, MST, and the other of the magnet unit andthe armature unit is provided on the side of the movable surface of thestage PST, MST.

The reaction force, which is generated in accordance with the movementof the substrate stage PST, may be mechanically released to the floor(ground) by using a frame member so that the reaction force is nottransmitted to the projection optical system PL. The method for handlingthe reaction force is disclosed in detail, for example, in JapanesePatent Application Laid-open No. 8-166475 (corresponding to U.S. Pat.No. 5,528,118), contents of which are incorporated herein by referencewithin a range of permission of the domestic laws and ordinances of thestate designated or selected in this international application.

The reaction force, which is generated in accordance with the movementof the mask stage MST, may be mechanically released to the floor(ground) by using a frame member so that the reaction force is nottransmitted to the projection optical system PL. The method for handlingthe reaction force is disclosed in detail, for example, in JapanesePatent Application Laid-open No. 8-330224 (corresponding to U.S. Pat.No. 5,874,820), contents of which are incorporated herein by referencewithin a range of permission of the domestic laws and ordinances of thestate designated or selected in this international application.

As described above, the exposure apparatus EX according to theembodiment of the present invention is produced by assembling thevarious subsystems including the respective constitutive elements asdefined in claims so that the predetermined mechanical accuracy, theelectric accuracy, and the optical accuracy are maintained. In order tosecure the various accuracies, those performed before and after theassembling include the adjustment for achieving the optical accuracy forthe various optical systems, the adjustment for achieving the mechanicalaccuracy for the various mechanical systems, and the adjustment forachieving the electric accuracy for the various electric systems. Thesteps of assembling the various subsystems into the exposure apparatusinclude, for example, the mechanical connection, the wiring connectionof the electric circuits, and the piping connection of the air pressurecircuits in correlation with the various subsystems. It goes withoutsaying that the steps of assembling the respective individual subsystemsare performed before performing the steps of assembling the varioussubsystems into the exposure apparatus. When the steps of assembling thevarious subsystems into the exposure apparatus are completed, theoverall adjustment is performed to secure the various accuracies as theentire exposure apparatus. It is desirable that the exposure apparatusis produced in a clean room in which, for example, the temperature andthe cleanness are managed.

As shown in FIG. 9, the microdevice such as the semiconductor device isproduced by performing, for example, a step 201 of designing thefunction and the performance of the microdevice, a step 202 ofmanufacturing a mask (reticle) based on the designing step, a step 203of producing a substrate as a base material for the device, an exposureprocess step 204 of exposing the substrate with a pattern of the mask byusing the exposure apparatus EX of the embodiment described above, astep 205 of assembling the device (including a dicing step, a bondingstep, and a packaging step), and an inspection step 206.

According to the present invention, the bubble-suppressing unit, whichsuppresses the generation of the bubble in the liquid between theprojection optical system and the substrate, is provided. Accordingly,the exposure process can be performed in the state in which no bubble ispresent in the liquid on the optical path for the exposure light beam.Therefore, it is possible to avoid the deterioration of the patternimage which would be otherwise caused by the bubble. Further, it ispossible to produce a device having a high pattern accuracy.

1. A pattern formation method comprising the steps of: forming a resistfilm on a substrate; performing pattern exposure by selectivelyirradiating said resist film with exposing light with a liquid providedon said resist film; developing said resist film after the patternexposure; and recycling said liquid used in the step of performingpattern exposure.
 2. The pattern formation method of claim 1, whereinsaid liquid provided on said resist film comprises at least one of afresh liquid, or said recycled liquid.
 3. The pattern formation methodof claim 1, wherein said liquid is recycled during the next patternexposure.
 4. The pattern formation method of claim 1, wherein therecycling step has a sub-step of removing an impurity from the liquid.5. The pattern formation method of claim 4, wherein said liquid passesthrough a filter in the sub-step of removing an impurity.
 6. (canceled)7. The pattern formation method of claim 3, further comprising a step ofremoving an impurity mixed in said liquid having been recovered afterthe pattern exposure.
 8. The pattern formation method of claim 7,wherein said liquid passes through a filter in the step of removing animpurity.
 9. (canceled)
 10. The pattern formation method of claim 1,further comprising, before or after the step of performing patternexposure, a step of removing an impurity mixed in said liquid.
 11. Thepattern, formation method of claim 10, wherein said liquid passesthrough a filter in the step of removing an impurity.
 12. (canceled) 13.The pattern formation method of claim 1, further comprising, after thestep of performing pattern exposure, a degassing step of removing a gasincluded in said liquid.
 14. The pattern formation method of claim 1,wherein said liquid is water or perfluoropolyether.
 15. The patternformation method of claim 1, wherein said exposing light is KrF excimerlaser, ArF excimer laser or F₂ laser.
 16. A semiconductor fabricationapparatus comprising: a unit for providing a liquid between a resistfilm formed on a substrate and an exposure lens; a liquid supply sectioncoupled to said unit to provide said liquid to said unit; and arecycling unit coupled to said unit for receiving said liquid from saidunit and for purifying said liquid, wherein said recycling unit iscoupled to said liquid supply section to transfer said purified liquidto said liquid supply section. 17.-20. (canceled)
 21. The semiconductorfabrication apparatus of claim 16, further comprising a degassingsection provided between said liquid supply section and said unit, forremoving a gas included in said liquid to be supplied to said unit. 22.The semiconductor fabrication apparatus of claim 16, wherein saidrecycling unit has a filter for removing said impurity included in saidliquid.
 23. The semiconductor fabrication apparatus of claim 16, whereinsaid impurity is particles. 24.-26. (canceled)
 27. The semiconductorfabrication apparatus of claim 16, wherein said liquid is water orperfluoropolyether.
 28. The semiconductor fabrication apparatus of claim16, wherein said exposure section uses, as exposing light, KrF excimerlaser, ArF excimer laser or F₂ laser.
 29. The semiconductor fabricationapparatus of claim 16, said unit is placed in a pattern exposuresection.
 30. A semiconductor fabrication apparatus comprising: a unit toprovide a liquid between a resist film formed on a substrate and anexposure lens; a liquid supply section that is connected to said unit toprovide said liquid for said unit; a degas section provided between saidliquid supply section and said unit to remove a gas included in a liquidprovided from said liquid supply section, an impurity removal unit thatis connected to said unit to remove an impurity included in said liquidflowed from said unit, wherein said impurity removal unit is connectedto said liquid supply section to transfer a liquid from which saidimpurity has been removed, for said liquid supply section. 31.-32.(canceled)
 33. The semiconductor fabrication apparatus of claim 30,wherein said impurity removal unit has a filter for removing saidimpurity included in said liquid. 34.-35. (canceled)
 36. The patternformation method of claim 1, wherein the substrate and the resist formedthereon are fully submerged in the liquid during the pattern exposure.37. The semiconductor fabrication apparatus of claim 16, wherein thesubstrate and the resist formed thereon are fully submerged in theliquid in an exposure section having the exposure lens.
 38. Thesemiconductor fabrication apparatus of claim 30, wherein the substrateand the resist formed thereon are fully submerged in the liquid in anexposure section having the exposure lens.
 39. The pattern formationmethod of claim 1, wherein the liquid is only deposited on a surface ofthe resist during the pattern exposure.
 40. The semiconductorfabrication apparatus of claim 16, wherein the liquid is only depositedon a surface of the resist at an exposure section having the exposurelens.
 41. The semiconductor fabrication apparatus of claim 30, whereinthe liquid is only deposited on a surface of the resist at an exposuresection having the exposure lens.
 42. A semiconductor manufacturingapparatus comprising: a stage having a substrate on which a resist filmis formed; a liquid supplying section for providing a liquid onto saidstage; an exposing section which irradiates said resist film withexposing light through a mask with said liquid provided on said resistfilm; and a removing unit which removes a gas included in said liquid.43. The semiconductor manufacturing apparatus of claim 42, wherein saidremoving unit degases said liquid supplied onto said resist film and isdisposed between said liquid supplying section and said exposing sectionor within said liquid supplying section.
 44. (canceled)
 45. Asemiconductor manufacturing apparatus comprising: a stage having asubstrate on which a resist film is formed; a liquid supplying sectionfor providing a liquid onto said stage; an exposing section whichirradiates said resist film with exposing light through a mask with saidliquid provided on said resist film; and a degassing section whichremoves a gas included in said liquid,  wherein said degassing sectionincludes: a removing part which removes a gas from said liquid havingbeen provided from said liquid supplying section; a first supplying pathwhich provides, onto said resist film, said liquid from which said gashas been removed; and a second supplying path which provides, to saidremoving part, said liquid having been provided onto said resist film.46. A semiconductor manufacturing apparatus comprising: an exposingsection which irradiates, with exposing light through a mask, a resistfilm formed on a substrate, with a liquid provided on said resist film;a supplying section which provides said liquid between said resist filmand said exposing section; a collecting section which collects saidliquid having been supplied onto said resist film; and a controllingsection which controls a liquid supplying operation of said supplyingsection, a liquid collecting operation of said collecting section and anoperation of a stage having said substrate.
 47. The semiconductormanufacturing apparatus of claim 46, wherein said controlling sectioncontrols the liquid supplying operation and the liquid collectingoperation and adjusts the operation of said stage in such a manner thata flow rate and a flowing direction of said liquid caused on said resistfilm by the liquid supplying operation and the liquid collectingoperation substantially accord with a movement rate and a movingdirection of said stage.
 48. The semiconductor manufacturing apparatusof claim 45, wherein said liquid collected through said second supplyingpath to said removing part is degassed in said removing part andprovided onto said resist film through said first supplying path. 49.The semiconductor manufacturing apparatus of claim 46, wherein saidcollecting section and said supplying section are mutually connected,and said liquid having been collected by said collecting section flowsinto said supplying section.
 50. The semiconductor manufacturingapparatus of claim 45, wherein said liquid is composed of water orperfluoropolyether.
 51. The semiconductor manufacturing apparatus ofclaim 45, wherein said exposing light is KrF excimer laser, ArF excimerlaser or F₂ laser. 52.-56. (canceled)
 57. A pattern formation methodcomprising the steps of: forming a resist film on a substrate;irradiating selectively said resist film with exposing light with aliquid provided on said resist film; and forming a resist pattern bydeveloping said resist film after the pattern exposure, wherein the stepof performing pattern exposure includes a sub-step of removing a gasincluded in said liquid provided on said resist film.
 58. The patternformation method of claim 57, wherein said liquid is composed of wateror perfluoropolyether.
 59. (canceled)
 60. The pattern formation methodof claim 57, wherein said exposing light is KrF excimer laser, ArFexcimer laser or F₂ laser.
 61. A pattern formation method comprising thesteps of: forming a resist film on a substrate; irradiating selectivelysaid resist film with exposing light with a liquid provided on saidresist film; and forming a resist pattern by developing said resist filmafter the pattern exposure, wherein the step of performing patternexposure includes a sub-step of supplying said liquid onto said resistfilm and collecting said liquid from on said resist film in such amanner that a flow rate and a flowing direction of said liquid caused onsaid resist film substantially accord with a movement rate and a movingdirection of said stage.
 62. The pattern formation method of claim 61,further comprising a step of removing a gas from said liquid having beencollected from on said resist film and providing, onto said resist film,said liquid from which said gas has been removed.
 63. The patternformation method of claim 61, wherein said exposing light is KrF excimerlaser, ArF excimer laser or F₂ laser. 64.-67. (canceled)